1. Field of the Invention
The present invention relates to an electromagnetically operated switch, and more particularly to an electromagnetically operated switch which is applicable to a starter device for starting the engine of a vehicle.
2. Discussion of the Background
The electromagnetically operated switch in the starter device is used to drive a shift lever for sliding a pinion, and further to apply power to a D C motor of the starter device. Such electromagnetically operated switch is constructed as shown in FIG. 4.
The electromagnetically operated switch 1 includes a cylindrical casing 2 which has a wall 2a at its one end. In the casing 2 is arranged a cylindrical bobbin 4 which has an exciting coil 3 wound in its peripheral annular recess. In the bobbin 4 is engaged a sleeve 5, inside of which a fixed core 6 and a plunger 7 as a movable core are arranged to confront each other. The fixed core 6 is integrally provided with a flange 6a, which expands outwardly in the radial direction. The flange is in close contact with an end surface of the bobbin 4. A cup-shaped cap 8 is mounted to the end surface of the flange 6a remote from the bobbin 4, keeping its open end in close contact with the end surface. Between the open end of the cap 8 and the end surface of the flange 6a is interposed a ring-like rubber packing 9 to seal the joint portion of the flange 6a and the cap 8, thereby preventing gas evolved from the exciting coil 3 from invading the inside (contacting chamber) of the cap 8.
Fixing the cap 8 to the end surface of the flange 6a of the fixed core 6 has been made by putting the peripheral portion of the flange 6a and the peripheral portion 8a of the open end of the cap 8 in the casing 2 and bending the marginal portion of the casing 2 toward the end surface of the peripheral portion 8a of the cap 8 to crimp the marginal portion of the casing 2. In this way, the bobbin 4, the fixed core 6 and the cap 8 are fixed together to the casing 2.
At the central portion of the fixed core 6 is formed a through bore, in which a rod 10 is slidably inserted having its one end projected toward the plunger in a predetermined length. The other end of the rod 10 which projects in the inside of the cap 8 supports a movable contact 11. The cap 8 has a fixed contact 12 mounted thereon at a position where it can get in touch with the movable contact 11 when the rod 10 has been shifted.
In FIG. 4, reference numeral 13 designates a piston-shaped hook which is arranged to be slidable in a recess of the plunger 7, which opens outwardly in the axial direction. Reference numeral 14 designates a return spring which is arranged between the fixed core 6 and the plunger 7 in a compressed state. Reference numeral 15 designates a spring which urges the rod 10 to return it to a predetermined position.
When the electromagnetically operated switch is applied to the starter device, the switch could be generally splashed water by a wheel during the vehicle driving to be drenched owing to its mounting position (it is mounted to the engine). In this case, the conventional switch 1 can prevent the gas evolved from the exciting coil 3 from invading the contacting chamber because the packing 9 is sandwiched between the open end of the cap 8 and the flange end surface when the cap 8 is mounted to the flange end surface of the fixed core 6. However, the water which has gotten into the sleeve passes in the through bore of the fixed core 6 along the rod 10 and invades the inside of the cap 8. In general, the sleeve 5 and the return spring 14 are made of stainless steel or the like, the plunger 7 and the rod 10 are greased, and the fixed core 6 is plated. Although anticorrosive treatment is given to some parts in this way, no treatment is given to the movable contact 11 and the fixed contact 12 in terms of conductivity, both contacts being made of copper.
As result, when water comes into the contacting chamber, the movable contact 11 or the fixed contact 12 will rust away, creating troubles wherein conduction becomes poor or the water causes a leak current.